I've been perusing their website for a little while now, and there is a rough pattern:

At least for acoustics:

• The first two letters are the series. This is the most variable component, but follows some loose guidelines:
  • The initial letter is often indicative of what what onboard electronics that series of guitar comes with, even if the particular guitar doesn't have them (C guitars come with Fishman CD-1, F come with Fender, P come with Fender/Fishman sonitone plus). This letter is sometimes omitted (see the simple D10 dreadnought)
  • The second (or first, if there is only one) letter generally indicates the body style. D is dreadnought, C is concert, B is bass (or banjo!), O is orchestra (?)
• The number generally indicates quality. Bigger number more expensive within a series.
• S after the number indicates a solid top (no S indicates laminate)
• C after the number indicates a single cutaway body
• E at the end indicates that the guitar has onboard electronics